292 Intake Port Questions

[Motorfist]

Hello everyone and thanks in advance for your help. Even though I haven't met anyone from this forum in the real world, I've been lurking for years and have a lot of respect for the knowledge base here. I tend to ramble so feel free to skip a couple paragraphs...

My first vehicle was a 70 K10 that my father and I fixed up a bit when I was 15 and almost 35 years later I am looking to share that same nostalgic feeling with my sons. I am fairly capable "parts changer" as I call it and always wanting to be a decent mechanic. I've swapped a few motors but never actually rebuilt one myself and I am starting to get in to that stage. More on that for another day...

I am working on a put around truck which is a 68 c19 LWB with a 292, Rochester Monojet and sm465 trans. My younger son will drive this as we build a 72 k10 project starting later this summer. The truck has been parked for 3 years and I started it rarely since we've owned it as it wasn't road worthy when I bought it. I don't recall how long it sat before that. I "rebuilt" the carb and front end to get it road worthy and have put about 100 miles on it since. It runs but fairly crappy and that catches us up to today.

I checked the compression last week wanting to make sure I shouldn't just swap in another 350 before I started tune up efforts.

Cyl 1 - 125
2 - 130
3 - 130
4 - 135 (wet spark plug)
5 - 135
6 - 130

I was pleasantly surprised with that so I ordered the last bits I needed to do a HEI swap and also the Felrpo manifold gasket kit. I had noticed 1st, 2nd 5th and 6th bolts that hold the manifolds on were loose and the valve in the heat riser was stuck. Also the drivers side bolt that joins the manifolds at the heat riser was gone, assumed broke off. I have a spare parts truck with another 292 and planned to steal the exhaust manifold off of it as it looks to be in great shape.

I took the manifolds off the 68 today and was happy to find that the mentioned bolt was missing and not broke off and even happier to find that the was a broken bolt wedged against the weight on the heat riser. Once I removed that it moves just fine!

However I noticed that the 3rd/4th intake port was wet and the 5th/6th even more so. I am surprised to see this with the compression numbers as good as they are. Is this somewhat normal given all the above info and I should proceed with the tune up or is this cause for alarm?

[Grumpy old man]

Clean it all up check all vacuum hoses finish HEI install , Make sure the passages between the intake and exhaust manifolds are cleaned of carbon bolt it all back together with new gaskets , repair the temp sending wire and drive it ,

['68OrangeSunshine]

Nice compression numbers. These Big L6 Blocks will run a long time if you hit all their sweet spots right.

[Motorfist]

Awesome guys thank you! Hopefully, I will report back with a smooth running truck in the next few days.

[Steeveedee]

Replace those freeze plugs in the head and block before you put that manifold back on! The one below cylinders 1&2 appears to be blistered enough that it's going to leak right after you put the manifold on. Then it's going to be a pain in the neck task.

[Motorfist]

That one is partially clean because i was able to hit it with the pressure washer but it still has some gunk on it. I will clean them up and take some better pics and maybe you can help me confirm they need replaced?

[May70]

Saw your post last night, usually its a good idea in my general experience to start a new thread (as you did). Case in point my forum thread has definitely had a 'paper trail' tracing down some things. No telling where you will end up on these, ha ha. Funny someone mentioned, he thought I had 292 (numerical value amount) questions.. turns out I just might

Was there oil in the intake manifold? Its my understanding you will get higher(false) compression readings if oil is leaking into the cylinder via rings/seals and is helping the rings seal, causing increased compression. Or in extreme cases there is so much oil in the cylinder it is actually decreased the volume enough to increase pressure (probably not the case here just a statement).

If your manifold has the nipple from the valve cover (pcv), ensure you have baffles of some sort. Steeveedee pointed that one out to me on my setup. I believe a am getting some oil into the manifold via that pathway....

Another thing to consider with 5/6 being 'wetter' ( i assume you mean with oil) than 3/4 is that the motor is mounted with a bit of an angle and if oil is getting into your manifold it could be running down the back 2 intake holes.

3/4 plugs were the worst on my truck and it so happens that is where the oil was sitting in my intake as you probably saw. Im hoping its just oil passing through those hoses but it wouldn't surprise me if the valve seals are gone.

Is it smoking? If its not smoking I doubt oil leakage into cylinders (causing false compression reading) is the case. If no smoke I wouldn't worry about it with those compression numbers. Im not super knowledgeable though.

Also in the pics I see a stud in place of where a bolt should be, maybe you said it and ive missed it but that head has been off before and odds are they had a little bit of trouble so just be ready and careful if you go to take it off.

[Motorfist]

Originally Posted by Steeveedee

Replace those freeze plugs in the head and block before you put that manifold back on! The one below cylinders 1&2 appears to be blistered enough that it's going to leak right after you put the manifold on. Then it's going to be a pain in the neck task.

What do you think of these Steve? They don't look deformed or anything to me but maybe I don't know any better?

Also I see 1970 is cast in to the block. I am guessing that's a date and not an arbitrary number so I guess the motor is not the original?

[Motorfist]

Originally Posted by May70

Saw your post last night, usually its a good idea in my general experience to start a new thread (as you did). Case in point my forum thread has definitely had a 'paper trail' tracing down some things. No telling where you will end up on these, ha ha. Funny someone mentioned, he thought I had 292 (numerical value amount) questions.. turns out I just might

Was there oil in the intake manifold? Its my understanding you will get higher(false) compression readings if oil is leaking into the cylinder via rings/seals and is helping the rings seal, causing increased compression. Or in extreme cases there is so much oil in the cylinder it is actually decreased the volume enough to increase pressure (probably not the case here just a statement).

If your manifold has the nipple from the valve cover (pcv), ensure you have baffles of some sort. Steeveedee pointed that one out to me on my setup. I believe a am getting some oil into the manifold via that pathway....

Another thing to consider with 5/6 being 'wetter' ( i assume you mean with oil) than 3/4 is that the motor is mounted with a bit of an angle and if oil is getting into your manifold it could be running down the back 2 intake holes.

3/4 plugs were the worst on my truck and it so happens that is where the oil was sitting in my intake as you probably saw. Im hoping its just oil passing through those hoses but it wouldn't surprise me if the valve seals are gone.

Is it smoking? If its not smoking I doubt oil leakage into cylinders (causing false compression reading) is the case. If no smoke I wouldn't worry about it with those compression numbers. Im not super knowledgeable though.

Also in the pics I see a stud in place of where a bolt should be, maybe you said it and ive missed it but that head has been off before and odds are they had a little bit of trouble so just be ready and careful if you go to take it off.

Thanks for popping over to check this out! I learned a lot from your thread. There isn't pooled oil in my intake per say, just a bit of a coating. I agree that the front intake ports were dry due to the angle of the engine.

I do have the baffles inside the valve cover and the truck doesn't smoke so that's a plus.

I didn't even notice that head stud until you pointed it out so nice catch. I figured someone had messed with it at least a little before as the valve cover and inspections covers had been removed and painted. Now with the 1970 block casting I am thinking it's likely not even the original motor. Does your block have a date cast in to it?

[Steeveedee]

Originally Posted by Motorfist

What do you think of these Steve? They don't look deformed or anything to me but maybe I don't know any better?

Also I see 1970 is cast in to the block. I am guessing that's a date and not an arbitrary number so I guess the motor is not the original?

I guess I'd need X-ray vision to see what they look like on the other side. They look OK from this side. But those plugs only cost $14 for the whole engine, in brass.

https://www.napaonline.com/en/search...=nol-veh-conds

['68OrangeSunshine]

Motorfist -- Is there a ''dress code'' stamped into the machined pad right by the distributor hole? The 2- or 3-digit letters could give us a clue. And the first 4 didgts will tell us where and when it was assembled.
It it IS a 1968 engine, the "1970" casting mark might not be a date but a mold number, part number, or anything else.

[Motorfist]

Originally Posted by '68OrangeSunshine

Motorist -- Is there a ''dress code'' stamped into the machined pad right by the distributor hole? The 2- or 3-digit letters could give us a clue. And the first 4 didgts will tell us where and when it was assembled.
It it IS a 1968 engine, the "1970" casting mark might not be a date but a mold number, part number, or anything else.

I just checked and it has F0219UH stamped there.


Also, as I was cleaning the debris out of the intake and exhaust ports after scraping the gasket surface, I notice these metal tubes in the exhaust ports. They were in varying positions and the one for Cyl 1 has damage on the end. I removed the pipe plug that keeps it in the head and wasn't able to pull it out of the head because the end is damaged.

I searched and searched to try and figure out what they are because I was embarrassed to ask LOL. I came up with nothing other than noticed some heads don't even have them.

Are they supposed to keep the exhaust valves from traveling too far or something?

['68OrangeSunshine]

F0219UH.
Flint, Michigan
02 = February
19 = 19th
UH = 292 L6 w/manual trans '67,'68.
Sweet block.
I have one 292 I ran from Summer 1977 to Fall 2002. F0626UH. Came out of a '67 K/20 Forest Service long stepside. Laying fallow now after a 250,000 mile run. UH blocks predate the "1970" casting number. It's not a date code, but I've heard people claim their '68 truck has a '70 motor because of it.
The engine that was in my '68 C/10 when I bought it in June 1973, was F0627XAE. [To date no one has been able to decode "XAE.''] After a performance rebuild, that block is back in my Stepside.

Those tubes in the head were for the A.I.R. [Air Injection Reaction?] smog pump.
A belt-driven smog pump on the passenger side, sucked exhaust fumes from the exhaust manifold and pumped them back into the cylinders for a 're-burn' to cut down excess hydrocarbons. This assumed the average driver/owner did not keep the timing and ignition components in top condition. A well tuned engine will burn better and cleaner without that junk. Led to vapor lock and overheating from my experience.
But at least GM could pretend it was doing "something'' toward Cleaner Air.
They should be extracted and plugged. Whether they ever did any good for performance is a debatable subject. My own opinion is they were a political solution to a political problem. I ditched the A.I.R. system as soon as I left California.

[Motorfist]

Excellent info and thanks for the reply! Cool history on your 292's and the mystery about the XAE code. Crazy you've had it all this time and it's still unknown. That kind of stuff is cool to me.
I am becoming more interested with this engine daily. Guys that have them seem to really dig them!

All the A.I.R. holes are plugged but they left the tubes in them. I will remove them now and am glad they aren't needed.
Thanks again,
Josh

['68OrangeSunshine]

I re-edited my last post after you replied, to add a pic of my head. I used brass set screws with allen heads. I have headers. So I replaced the end studs with bolts, as headers need more clamping.
My guess on XAE is that it was an exchanged motor under warranty in the PO's first year.
Some of the senior pundits on this forum have puzzled over that dress number, but it's all lost in the shrouded mists of history by now.

[RichardJ]

>>orangesunshine,
A belt-driven smog pump on the passenger side, sucked exhaust fumes from the exhaust manifold and pumped them back into the cylinders for a 're-burn' to cut down excess hydrocarbons<<

Come on Sunshine, you should know better than that. You are right about the tubes being part of the A.I.R (Air Injection Reactor) system.
Putting Exhaust gases back into the cylinder combustion is what an EGR does and it does that to reduce Nox. Nox output is significantly increased when combustion temperature goes above 2500 deg. EGR gasses are introduced at specific times to keep temp below 2500.

A.I.R pumps fresh air into the exhaust manifold. When you have unburned gasses (hydrocarbons), plus heat and you add fresh air, the hydrocarbons burn harmlessly in the exhaust manifold.
The AIR system has no effect on the operation of the engine and the pump uses very little power to operate.

May70 & Motorfist.
The threaded studs in the 3rd hole in, from each end of the head are correct and original. Do not remove them. Sunshine mentioned the short studs in the end holes on both ends of the head. Those are also original. but can be unscrewed and replaced with longer threaded studs if using headers.

['68OrangeSunshine]

That's how it was explained to me, about 45 years ago. No one was enthusistic about using it anyway. Too late now.
No more A.I.R. and I don't miss it.
Apparently A.I.R. is still a debatable subject.
If I still lived in California, I'd be required to keep it. I don't.

[Steeveedee]

Originally Posted by '68OrangeSunshine

That's how it was explained to me, about 45 years ago. No one was enthusistic about using it anyway. Too late now.
No more A.I.R. and I don't miss it.
Apparently A.I.R. is still a debatable subject.
If I still lived in California, I'd be required to keep it. I don't.

Your truck is exempt from inspection in California, as is any vehicle produced before the 1976 year model. I see vehicles all the time with the AIR equipment gone and plugs in the ports in the manifolds or heads. If they were less than 25 years old, then yes indeed the requirement was to reinstall the equipment, a waiver could be had for those people who were unable to pay for that due to low income. I wrote waivers occasionally back in the day. For a '75 model year vehicle, the last year for inspection would have been 2000. California stopped the rolling drop off at 2001, so '76 model year and newer vehicles still get inspected biennially.

[Motorfist]

I had a few of the tubes slide right out and some would wiggle but not easily come out. A small angled pry bar wanted to bend them and not remove them.
So, I grabbed a phillips head screw driver with a shaft diameter just a bit larger than the tube I.D. and gently tapped it in to a stuck tube until it was wedged in. I was then able to just unscrew them out of the holes but turning the screw driver handle.

I got the manifolds reinstalled last night and hope to get some time to work on putting it back together today or tomorrow and a quick test drive before swapping the HEI in with the help if Shifty's thread.

You guys have bene very helpful, thanks!

Josh

['68OrangeSunshine]

Originally Posted by Steeveedee

Your truck is exempt from inspection in California, as is any vehicle produced before the 1976 year model. I see vehicles all the time with the AIR equipment gone and plugs in the ports in the manifolds or heads. If they were less than 25 years old, then yes indeed the requirement was to reinstall the equipment, a waiver could be had for those people who were unable to pay for that due to low income. I wrote waivers occasionally back in the day. For a '75 model year vehicle, the last year for inspection would have been 2000. California stopped the rolling drop off at 2001, so '76 model year and newer vehicles still get inspected biennially.

Oddly enough my '68 still requires an emissions inspection for registration each year in Arizona. Any vehicle '67 or later. No drop off. I usually pass with the L6, sometimes I have to change out the Jets and needles in my AFB type carb to a leaner setting. [Then after passing, dial it back up for performance.] I had a 454 in a '67 K/10 Suburban, that was a beast to get thru emissions. The 350 in my '71 Jimmy was usually a Bad Boy too. I found a loophole -- by getting a Year-Of-Manufacture license plate, AND collector car insurance, the truck becomes emissions exempt. I have a Yellow/Black 1971 [69-72] AZ plate for the GMC. It's also a cheaper reg fee. I have also acquired a White/Black [66-68] AZ plate from a board member. I could use it either on my '68 which is a daily driver, or use in on the '67 Suburban when I rebuild that.[But not the 454.]

[Steeveedee]

OK, I only know the California rules. Sucks to have to do the '68!

[Motorfist]

Well the truck is running much better now 👍🏻

After I removed the old AIR tubes I cleaned everything up and installed the new manifold gasket and manifolds. I then drove the truck just to see if that would make any improvements and nothing noticeable. The gasket needed replaced and everything needed properly reinstalled and it’s good to have that checked off the list. Also repaired the temp sending unit wire that was damaged.

Started the HEI swap but Had to take a break for a week for family stuff. I was able to get back out there today and finish it up and the truck runs sooo much smoother! I forgot to order a distributor gasket so it’s leaking a little oil there but will get that handled tomorrow when the parts store opens back up.

Thanks for you help gents, I really appreciate the advice!

Now, to see if I can adjust the clutch so it has more use than at the very end of the pedal release...